模拟恶性梗阻性黄疸患者梗阻段胆管弧度的^(125)I粒子条长度和活性对病变末端及中心区域剂量的影响

Effects of^(125)I seed strand with different length and activity under simulated biliary radian on terminal and central dose of the lesion

目的构建模拟恶性梗阻性黄疸患者梗阻段胆管弧度^(125)I粒子条的模型,评估粒子条长度和粒子活度对病变末端及病变中心区域剂量的影响。方法收集接受胆管支架联合^(125)I粒子条治疗的恶性梗阻性黄疸患者18例,利用三维治疗计划系统制作水模体,将水模体以DICOM格式导入放射性粒子源植入三维治疗计划系统。根据解超越方程计算18例患者的推算弧度,转换为折算弧度,取18例患者折算弧度的平均值85°定义为模型的弧度,18例患者胆管梗阻段长度的平均值45 mm定义为模型病变的长度。在水模体上勾画出弧度为85°、长度为45 mm的粒子条模型,粒子条由10颗粒子组成,即模型1;在粒子条的两端各加1、2、3、4颗粒子,形成模型2、3、4、5。将模型的粒子活度设置为0.5、0.6、0.7、0.8、0.9、1.0 m Ci,观察各个模型下病变末端及病变中心在粒子条向心侧及离心侧的剂量差异。结果在同一模型中,不同粒子活度间比较,病变末端和病变中心的向心侧、离心侧累积剂量均随粒子活度增加而增加。在同一粒子活度下,不同模型间比较,模型5病变末端和病变末端的向心侧、离心侧累积剂量均大于其他四种模型。在同一粒子活度及同一模型下,病变末端离心侧的累积剂量均大于向心侧的累积剂量,病变中心离心侧的累积剂量均小于向心侧的累积剂量。病变末端与病变中心的剂量差异度比较:在向心侧,模型1、2、3、4、5在不同粒子活度下的累积剂量差异度最大分别为74.94%、40.92%、26.74%、20.82%、17.90%,累积剂量的差异度随模型粒子条长度的增加而减小;在离心侧,模型1、2、3、4、5的最大差异度分别为5.20%、-11.38%、-16.71%、-19.34%、-20.68%,累积剂量的差异度随模型粒子条长度的增加而增大。结论基于病变长度为45 mm、弧度为85°的恶性梗阻性黄疸胆管病变模型,当支架位于粒子条的向心侧,在病变末端多加粒子,可降低病变末端和中心区域的累积剂量差异;当支架位于粒子条的离心侧,病变长度与粒子条长度相等时,差异最低。

Objective The model of^(125)I seed strand simulating the radian of bile duct of the obstructive part in patients with malignant obstructive jaundice was constructed.The effect of the length and activity of^(125)I seed strand on the terminal and central dose of the lesion was evaluated by treatment planning system(TPS).Methods Eighteen patients with malignant obstructive jaundice treated with bile duct stents combined with^(125)I seed strand were collected.The water phantom was made by three-dimensional TPS.The water phantom was imported into radioactive seed source and then was implanted into DICOM format.The calculated radians of 18 patients were calculated according to the solution transcendental equation and then were converted into converted radians.The average value of 85° of converted radians of 18 patients was defined as the radian of the model,and the average value of 45 mm of bile duct obstruction length of 18 patients was defined as the length of model lesions.We drew a seed strand model with an arc of 85° and a length of 45 mm on the water model.The model 1 was composed of 10 seeds.We added 1,2,3 and 4 seeds at both ends of the seed strand to form models 2,3,4 and 5.We set the seed activity of the model to 0.5,0.6,0.7,0.8,0.9 and 1.0 m Ci,and observed the dose difference of the lesion end and lesion center on the centripetal side and centrifugal side of the seed strand under each model.Results In the same model,the cumulative doses of centripetal and centrifuge side of lesion end and lesion center increased with the increase of seed activity.Under the same seed activity,the cumulative doses at the end of the lesion,the centripetal side and the centrifugal side in the model 5 were greater than those in the other four models.Under the same particle activity and the same model,the cumulative dose on the centrifugal side at the end of the lesion was greater than that on the centripetal side,and the cumulative dose on the centrifugal side in the center of the lesion was less than that on the centripetal side.On the centripetal side,the cumulative dose differences of models 1,2,3,4 and 5 under different particle activities were 74.94%,40.92%,26.74%,20.82%,and 17.90%,respectively.The cumulative dose differences decreased with the increase of the length of the model particle strip.On the centrifugal side,the maximum differences of models 1,2,3,4 and 5 were 5.20%,-11.38%,-16.71%,-19.34% and-20.68%,respectively.The difference of cumulative dose increased with the increase of model particle strip length.Conclusions Based on the malignant obstructive jaundice model with the lesion length of 45 mm and the radian of 85°,when the biliary stent is located on the centripetal side of the seed strand,adding seeds at the end of the lesion can reduce the cumulative dose difference between the end and the center of the lesion;when the biliary stent is located on the centrifugal side of the seed strand,the difference is the lowest when the lesion length is equal to the length of the seed strand.